Thiourea impregnated sealing compound



Patented Dec. 26, 1950 THIOUREA IMPREGNATED SEALING MPOUND Julius L.Schneider, Chicago, and Raymond J. Evans. Bensenville, Ill., aasilnorsto Continental Can Company, Incorporated, New York, N. Y., a corporationof New York No Drawing. Application June 5, 1946, Serial No. 674,648

8 Claims. (Cl. 260-174) The following specification relates to ourinvention in improvements in corrosion inhibiting compositions asapplied to metal containers for food products and other compounds whichare apt to corrode the metal lining of the container.

Food containers such as tin plated metal cans are generally satisfactorywith many food compounds and the like which by their nature do notattack the tin plate lining of the cans. However, there is aconsiderable number of products having slightly acid character whichhave a tendency to attack the tin plate and corrode the foundationmetal. This is particularly true at the seams which have been made inthe process of forming or closing the container. and where the inner tinplate has been impaired by bending or abrasion.

The provision in such a container of a source of corroding inhibitingcomposition has been suggested. For example, the prior patent ofStevenson and Flugge granted August 1, 1939, No. 2,168.107, discloses asheet metal container in which a plastic sealing compound within theseams contains an inhibiting substance. However, no special provisionhas been made to regulate the discharge or insure the maximumavailability of the inhibitor during storage.

It is a principal object of our invention to provide a sealingcomposition of such a container with a suitable inhibitor having amaximum availability and thus permitting a reduction in actual quantityof the inhibitor present.

It is a further object of our invention to increase the availability ofthe inhibitor to more than what is localized in the surface of thesealing compound. In this way the capsuling effect of the plasticcomposition is overcome. and more of the inhibiting composition renderedavailable.

A still further object of the invention is to insure a gradual leachingeffect or discharge. Thus the inhibitor is supplied over a period ofseveral weeks after the can is filled and sealed and hence any corrosiveactivity becoming evident in the product during storage will beimmediately met and counteracted and the corrosion of the tin plateinhibited.

We have set out in the following description the preferred mode ofattaining the above objects and others which will be readily apparent.

It is usual to provide a sealing composition, essentially a rubber-likematerial compounded with a resin, zinc oxide, anti-oxidants, carbonblack and other commonly used ingredients. Such a sealing compound isapplied to the groove and curl of the can end so that it will form aneffective hermetic seal after being closed.

As pointed out in the above mentioned patent, such a sealing compositionmay be the medium by which an inhibiting compound is supplied. Wherethis compound is added to the sealing composition direct, much of thecompound is contained uniformly distributed in the body of the sealingcomposition and not readily available at the surface. This may be calleda capsuling effect and as a consequence only a minor proportion of theinhibiting compound is available to be taken up by the contents of thecan during packing and storage.

To increase the availability of the inhibitor, it is our purpose touniformly disperse in the sealing composition a fibrous absorbent whichis impregnated with the inhibiting compound. As the fibers extendinwardly from the surface of the layer of sealing compound, they have awicking effect so that the liquids contained in the can will dissolveand release the inhibiting compound with which the absorbent fibers maybe impregnated.

Finally, it is found that the addition of a dissolved resin to thefibers permits its more effective dispersion in the dough.

A suitable inhibiting compound may be prepared by dissolving thiourea inacetone and water. This may then be taken up by saturating celluloseflock with the solution. It is desirable to use flock in which the alphacellulose is equal to 92% or better. The ratios used are as: follows:

Range of parts by weight Fibrous absorbent (cellulose flock, 92 per centalpha), 63.0 lb 30 to 75 Thiourea, 12 lb to Acetone, 32.0 lb to Water,14.0 lb u 10 to 20 To the saturated flock there is then added syntheticresin dissolved in a suitable petroleum solvent. The mixture should thenbe stirred briefly. For this resin solution we use the followingmaterials;

Range of parts by weight Resin (Piccolyte 5-115), 12.0 lb 8 to 20Solvent (Skellysolve B), 190.0 lb..... to 225 The above mixture is thencombined with a milled mixture of rubber-like material preferablycompounded as follows:

Ratio to rubber Rubber (GR-S), 30.0 lb Resin (Piccolyte 8-115), 4.0 lb 1to 8 Zinc oxide, 54.0 lb 2 to 1 Antioxidant (Agerite White), 0.6 lb 1to4% Carbon black, 0.15 lb 0 to 0.5

aeeaeee The rubber is added to the impregnated fiber and resin solutionwhich is then stirred until the dispersion is uniform. This may takefrom 2% to .30 hours at room temperature. The resulting compound may bestrained through suitable filter equipment and stored in air-tight drumsuntii used without sufiering loss or prop= erties.

There will be a total of 42 to 44% by weight of solids in the abovecomposition.

After application to the container surface and drying, the dried sealingcompound will have the following approximate percentage composi- Assuggested above, this compound may be spread thinly upon the groove andcurl of the container end and also upon the side seam of the container.After the end is seamed to the container, the compound forms a hermeticseal.

The watery contents of the can in contact with the sealing compound willgradually dissolve the inhibiting compound and leach it out. It has beenobserved that perhaps 20% of the inhibitor is thus leached out in thefirst two weeks of storage.

Under such circumstances the inhibitor pro tects the metal from attackby acid contents of the container. Typical acid contents may beapple-sauce, apple juice, strawberries, sour cherries or other acidfruits.

The sealing compound containing the saturated fiber has a slightlyroughened hispidulous surface due to the fact that the fiber projectsslightly from. the surface. This is, of course, not snmcient tointerfere with the sealing efiect. However, it promotes the availabilityof the in= hibiting compound present.

The formula for the inhibitor impregnated absorbent may vary within awide range. While we have suggested the use of alpha cellulose flock of2% mesh, other absorbent fibrous materials may be substituted such asfinely ground wood fiber and the like.

As pointed out in the above identified patent, thiourea is one oiseveral inhibitors found suitable ior this purpose, and any of these andamalogous compounds may be used in the present instance.

As a solvent for the inhibitor we may substitute other aliphaticalcohols such as methanol and isopropyl alcohol.

In compounding the synthetic resin we have used Piccolyte 8-115 which isa pure hydrocarbon terpene resin having a melting point of 239 F.However, it may be replaced by ester gum which is a glyceryl ester ofrosin, melting point 200 F. and acid number 6 to 8. This will alsosuggest other analogous resins suitable for this purpose.

Agerite white is the trade name for aldolalpha naphthyl amine (CondensedChemical Dictionary. 1942) The Skellysolve B is a petroleum solventhaving a boiling range of 145 to 160 F.

For this there may be substituted higher boil-.- ing' solvents such assolvent naphtha B boiling from 160 to. 240 F.

In place of the GR-S rubber we may also use natural rubber, butyl rubberand the like commonly known substitutes.

In place of zinc oxide we may use alumina and tor antioxidant anysuitable one such as Flectol H (condensation product of acetone-aniline)is suitable.

The addition of the inhibiting substance to the sealing dough by meansof an absorbent fiber forms a very convenient means of ensuring anadequate supply for discharge into the can contents. The inhibitor isleached out gradually as needed. The leaching continues until the majorpart of the available inhibitor is thus ren dcred available to thecontents of the can. As a consequence the use of a sealing compositioncontaining two parts of thiourea per one million parts of the volume ofthe can is found to be as efl'ective as six parts per million when thethiourea is compounded with the sealing dough without fiber. Expressedin another way, more of the thiourea is actually made available for useand hence less has to be incorporated in the sealing compound.

As indicated above, the corrosion inhibiting composition may becompounded of a considerable number of diflerent ingredients and stillcome within the scope of the invention as defined in the followingclaims:

What we claim is:

1. A can sealing composition for inhibiting corrosion comprising arubbery hydrocarbon plastic sealing compound insoluble in watercontaining suflicient fibrous porous'ccllulosic absorbent uniformlydistributed therein to be partially exposed at its surface when spread,said absorbent being impregnated with thiourea.

2. A can sealing composition for inhibiting corrosion comprising arubbery hydrocarbon plastic sealing compound insoluble in watercontaining sufllcient fibrous porous cellulosic absorbent uniformlydistributed therein to form an hispidulous surface when spread, saidabsorbent being impregnated with thiourea.

3. A can sealing composition for inhibiting corrosion comprising arubbery hydrocarbon plastic sealing compound insoluble in watercontaining suflicient cellulosic flock uniformly distributed therein tobe partially exposed at its surface when spread, said flock beingimpregnated with thiourea.

4. A can sealing composition for inhibiting corrosion comprising arubbery hydrocarbon plastic sealing compound insoluble in watercontaining suiificient cellulosic flock uniformly distributed therein tobe partially exposed at its surface when spread, said flock beingimpregnated with thiourea in approximately seven per cent of the totalweight.

5. A can sealing composition for inhibiting corrosion containing arubbery hydrocarbon plastic sealing compound insoluble in water, acompatible resin insoluble in water, zinc oxide and sumcientthiourea-impregnated cellulosic flock to appear partially exposed on thesurface of the composition when thinly spread.

6. A can sealing composition for inhibiting corrosion containing arubbery hydrocarbon plastic sealing compound insoluble in water, acompatible resin insoluble in water, zinc oxide, acetone, water, andsufllcient thiourea-impregnated cellulosic flock to appear partiallyexposed on the surface of the composition when thinly spread.

7. A can sealing composition for inhibiting corrosion containingapproximately 17 parts by weight or a rubbery hydrocarbon plasticsealing compound insoluble in water; 9 parts or a compatible resininsoluble in water; 31 parts of zinc oxide, 36 parts of cellulosic flockimpregnated 5 with 7 parts of thiourea, and fractional parts each ofantioxidant and carbon black.

8. A spreadable can sealing composition for inhibiting corrosioncontaining approximately 17 parts by weight or a rubbery hydrocarbonplastic substance, 9 parts or a compatible resin insoluble in water, 31parts of zinc oxide, 36 parts of a fibrous absorbent impregnated with 7parts of thiourea, and at least 100 parts by weight of a volatilehydrocarbon solvent.

JULIUS L. SCHNEIDER. RAYMOND J. EVANS.

6 REFERENCES orrnn The following references are of record in the NumberName Date 1,039,802 Randel Oct. 1, 1912 1,478,782 Dewey et a1 Dec. 24,1923 2,052,582 Robinson Sept. 1, 1936 2,148,862 Kern Feb. 28, 19392,168,107 Stevenson et a1 Aug; 1, 1939 2,320,716 Corkery June: 1. 1943

1. A CAN SEALING COMPOSITION FOR INHIBITING CORROSION COMPRISING ARUBBERTY HYDROCARBON PLASTIC SEALING COMPOUND INSOLUBLE IN WATERCONTAINING SUFFICIENT FIBROUS POROUS CELLULOSIC ABSORBENT UNIFORMLYDISTRIBUTED THEREIN TO BE PARTIALLY EXPOSED AT ITS SURFACE WHEN SPREAD,SAID ABSORBENT BEING IMPREGNATED WITH THIOURES